Human corneal endothelial cells do not divide in vivo. The failure of keratoplasty on human corneas is, therefore, in most cases, a failure of the endothelium of the graft. We hope ultimately to replace the diseased, old, corneal endothelium of the graft with a vigorously growing and functional endothelium which has previously been grown and maintained in tissue culture and which originates either from fetal human cornea (homologous implant) or from bovine cornea (heterologous implant). We also plan to test the ability of the endothelial or other organs (vascular) to substitute for the corneal endothelium. The technique used will be to grow the cells in vitro and to seed them back on corneas which either present diverse endothelial dystrophies or which have been denuded of their endothelium. Those corneas will then be grafted back either on the donor or on other species. Using the rabbit as an experimental animal, we will study the ability of corneal endothelial and bovine vascular cells to substitute for the rabbit corneal endothelium. Using the cat, a species in which the corneal endothelial cells do not proliferate in vivo, we will repeat these studies and compare the results to those obtained with cat corneal endothelial cells maintained in tissue culture. Next, using the monkey as an experimental animal, we will do similar studies, if the cat and rabbit studies have shown that such heterologous transplantation is viable. Since the final target is keratoplasty in the human, we will develop human corneal endothelial cell cultures from fetal corneas and use them in transplantation studies similar in design in those described in cat and rabbit. If bovine corneal endothelial cells have been shown to be viable for long periods of time in monkey or in cat, they may also be used. If the human or bovine vascular endothelium has been shown to be functional in maintaining cornial clarity, then human vascular endothelial cells could be transplanted on the cornea of the donor.